1. Field
The present disclosure relates to a method and a device for selecting a cell in a mobile communication system, and more particularly, to a method and a device for selecting a cell, which enable a base station to transmit data not only in a licensed frequency band but also in an unlicensed frequency band.
2. Description of Related Art
To meet the demand for wireless data traffic having increased since deployment of 4G communication systems, efforts have been made to develop an improved 5G or pre-5G communication system. Therefore, the 5G or pre-5G communication system is also called a ‘beyond 4G network’ or a ‘post LTE system’.
The 5G communication system is considered to be implemented in higher frequency (mmWave) bands, e.g., 60 GHz bands, so as to accomplish higher data rates. To decrease propagation loss of the radio waves and increase the transmission distance, beamforming massive multiple-input multiple-output (MIMO), full dimensional MIMO (FD-MIMO), array antenna, analog beamforming, and large scale antenna techniques are discussed in 5G communication systems.
In addition, in 5G communication systems, development for system network improvement is under way based on advanced small cells, cloud radio access networks (RANs), ultra-dense networks, device-to-device (D2D) communication, wireless backhaul, moving network, cooperative communication, coordinated multi-points (CoMP), reception-end interference cancellation and the like.
In the 5G system, hybrid FSK and QAM modulation (FQAM) and sliding window superposition coding (SWSC) as an advanced coding modulation (ACM), and filter bank multi carrier (FBMC), non-orthogonal multiple access (NOMA), and sparse code multiple access (SCMA) as an advanced access technology have been developed.
On the other hand, in the 3GPP that is in charge of cellular mobile communication standards, a new core network structure is called a 5G core (5GC), and the standardization thereof is in progress to achieve evolution from the existing 4G LTE system into a 5G system.
In comparison to an evolved packet core (EPC) that is a network core for the existing 4G, the 5GC supports the following discriminatory functions.
First, in the 5GC, a network slice function is introduced. In accordance with the 5G requirements, the 5GC should support various terminal types and services. For example, services provided in the 5G may include enhanced mobile broadband (eMBB), ultra-reliable low-latency communications (URLLC), and massive machine type communications (mMTC) services. Such terminals and services have different requirements with respect to the core network.
For example, the eMBB service may require a high data rate, whereas the URLLC service may require a high stability and low latency.
Technology proposed to satisfy such various service requirements is a network slice scheme. The network slice is a method for making several logical networks through virtualization of one physical network, and respective network slice instances (NSIs) may have different characteristics since they may have network functions (NFs) to match their characteristics. Accordingly, the 5G network can efficiently support several 5G services through assignment of the NSIs matching the characteristics of the required services to respective terminals.
Second, the 5GC can easily support network virtualization paradigms through separation of a mobility management function and a session management function from each other. In the existing 4G LTE, all terminals can be provided with services in the network through signaling exchanges with single core equipment called a mobility management entity (MME) that is in charge of registration, authentication, mobility management, and session management functions. However, in the 5G, the number of terminals is explosively increased, and the mobility and traffic/session characteristics that should be supported in accordance with the terminal types are sub-divided. In this case, if the single equipment, such as the MME, supports all the functions, scalability to add entities for necessary functions cannot help being deteriorated. Accordingly, in view of the function/implementation complexity of the core equipment that is in charge of a control plane and signaling load, various functions for scalability improvements have been developed based on a structure for separating the mobility management function and the session management function from each other.
In the LTE system, all IP traffics from terminals are anchored at a PDN-GW. Further, for latency improvement in a backhaul network, local IP access (LIPA) and selected IP traffic offloading (SIPTO) have been proposed to locate an IP anchor close to the terminal. In such a stnrcture, a PDN connection of the terminal is established, but there is no way to automatically establish or disconnect the PDN connection in accordance with the location of the terminal.
The present disclosure proposes a method for discovering a local area data network available in a place where a terminal is located, and establishing, disconnecting, or disabling a PDU session for connecting the data network of the terminal in accordance with the location of the terminal.